Randi B Weinstein

Interests

Teaching

Reproductive Endocrinology, Reproductive Physiology

Courses

Scholarly Contributions

Chapters

• Weinstein, R. B., Kawall, H., Hofmann, G. E., Fields, P. A., & Somero, G. N. (1998). Cold Adaptation and Stenothermy in Antarctic Notothenioid Fishes: What Has Been Gained and What Has Been Lost?. In Fishes of Antarctica. doi:10.1007/978-88-470-2157-0_8

Journals/Publications

• Weinstein, R. B. (2001). Terrestrial Intermittent Exercise: Common Issues for Human Athletics and Comparative Animal Locomotion1. American zoologist. doi:10.1668/0003-1569(2001)041[0219:tiecif]2.0.co;2
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  The earliest studies of intermittent exercise physiology noted that moving intermittently (i.e., alternating brief movements with brief pauses) could transform a heavy workload into a submaximal one that can be tolerated and sustained. The brief pauses that characterize intermittent locomotion permit at least partial recovery from prior activity. This research provided the foundation for the development of interval training and more recently for the re-evaluation of steady-state paradigms for comparative animal locomotion. In this paper I review key concepts underlying the performance of repeated activity. I provide examples from human athletics and training and comparative animal locomotion. To explore the limits of intermittent exercise performance, I examine the performance limits for continuous exercise and the rate and extent of the recovery of performance capacity following activity. While it is evident that altering locomotor behavior (i.e., moving intermittently) can alter the capacity of an animal to perform work, mathematical models of intermittent exercise could predict strategies (i.e., exercise intensity, exercise duration, and pause duration) that will increase performance limits for intermittent activity.
• Weinstein, R., Tritschler, H., & Henriksen, E. (2001). Antioxidant alpha-lipoic acid and protein turnover in insulin-resistant rat muscle. Free Radical Biology and Medicine, 30(4). doi:10.1016/S0891-5849(00)00489-5
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  We have shown previously that the antioxidant alpha-lipoic acid (ALA) can stimulate glucose transport and can enhance the stimulation of this process by insulin in skeletal muscle from insulin-resistant obese Zucker rats. As insulin can also acutely activate general protein synthesis and inhibit net protein degradation in skeletal muscle, we hypothesized that ALA could directly affect protein turnover and also increase the effect of insulin on protein turnover in isolated skeletal muscle from developing obese Zucker rats. In epitrochlearis muscles isolated from obese Zucker rats, insulin (2 mU/ml) significantly (p < 0.05) increased in vitro protein synthesis (phenylalanine incorporation into protein) and decreased net protein degradation (tyrosine release), whereas a racemic mixture of ALA (2 mM) had no effect on either process. Interestingly, rates of protein synthesis in muscle from obese Zucker rats were substantially lower compared to those values observed in age-matched insulin-sensitive Wistar rats, whereas rates of protein degradation were comparable. Obese Zucker rats were also treated chronically with either vehicle or ALA (50 mg/kg/d for 10 d). Again, insulin significantly increased net protein synthesis and decreased net protein degradation in epitrochlearis muscles isolated from vehicle-treated obese Zucker rats; however, this stimulatory effect of insulin was not improved by prior in vivo ALA treatment. These results indicate that the previously described effect of the antioxidant ALA to increase insulin-stimulated glucose transport in skeletal muscle of obese, insulin-resistant rats does not apply to another important insulin-regulatable process, protein turnover. These findings imply that the cellular mode of action for ALA is restricted to signaling factors unique to the activation of glucose transport, and does not involve the pathway of stimulation of general protein synthesis and net protein degradation. © 2001 Elsevier Science Inc.
• Weinstein, R., & Full, R. (1999). Intermittent locomotion increases endurance in a gecko. Physiological and Biochemical Zoology, 72(6). doi:10.1086/316710
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  Nocturnal geckos can actively forage at low temperatures. A low minimum cost of locomotion allows greater sustainable speeds by partially offsetting the decrease in maximal oxygen consumption (VO2(max)) associated with low nocturnal temperatures. The nocturnality hypothesis (Autumn et al. 1997) proposes that the reduced cost of continuous locomotion is a shared, derived characteristic that increases the capacity to sustain locomotion at low temperatures. Yet many lizards move intermittently at speeds exceeding those that elicit VO2(max). We exercised the frog-eyed gecko, Teratoscincus przewalskii, continuously and intermittently on a treadmill. At an exercise speed of 0.90 km h-1 (270% maximum aerobic speed), lizards alternating a 15-s exercise period with a 30-s pause period exhibited a 1.7-fold increase in distance capacity (total distance traveled before fatigue) compared with lizards exercised continuously at the same average speed (0.30 km h-1). The average aerobic cost of intermittent exercise was not significantly different from VO2(max). Locomoting intermittently could augment the increase in endurance resulting from the low minimum cost of continuous locomotion in nocturnal geckos. Intermittent behavior could increase the endurance of lizard movement in general.
• Weinstein, R. B. (1998). Effects of Temperature and Water Loss on Terrestrial Locomotor Performance in Land Crabs: Integrating Laboratory and Field Studies. American zoologist. doi:10.1093/icb/38.3.518
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  SYNOPSIS. Terrestrial and semi-terrestrial crustaceans are exposed to fluctuations in ambient temperature and conditions that favor evaporative water loss. These environmental stresses alter performance limits in the laboratory and behavior in the field. The maximal rate of oxygen consumption, maximum aerobic speed, and endurance capacity are greater at a body temperature (Tb) of 24°C than at 15°C or 30°C in the ghost crab, Ocypode quadrata . The total metabolic cost to move at the same relative speed is greater at a Tb of 24°C than at 15°C. Slower aerobic kinetics at 15°C result in a smaller relative contribution of oxidative metabolism to total metabolic cost. However, the relative contributions from accelerated glycolysis are similar at both temperatures. When locomotion is intermittent, the total distance traveled before fatigue can be similar at Tbs of 15 and 24°C but result from different movement and pause durations at these temperatures. Performance limits of the ghost crab are negatively affected by dehydration and are sensitive to rates of water loss. In the laboratory, endurance capacity of the fiddler crab, Uca pugilator, is greater at a Tb of 30°C than at 25°C. In the field, freely moving fiddler crabs with a Tb of 30°C travel at faster mean preferred speeds, as determined by motion analysis, than crabs at 25°C. Data for land crabs support and advance general ectothermic models for the effects of temperature and dehydration on locomotor performance.
• Weinstein, R., & Full, R. (1998). Performance limits of low-temperature, continuous locomotion are exceeded when locomotion is intermittent in the ghost crab. Physiological Zoology, 71(3). doi:10.1086/515927
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  Since a decline in temperature decreases aerobic capacity and slows the kinetics of exercise-to-rest transitions in ectotherms, we manipulated body temperature to better understand the performance limits of intermittent locomotion. Distance capacity (i.e., the total distance traveled before fatigue) of the ghost crab, Ocypode quadrata, was determined during acute exposure to 15°C inside a treadmill-respirometer. Instead of exacerbating the near-paralyzing effects of low body temperature resulting from the frequent transitions, intermittent locomotion allowed animals tO exceed the performance limits measured during steady-state locomotion. At low temperature, distance capacity for continuous locomotion at 0.04 m s-1 (83% maximum aerobic speed) was 60 m. When 30 s of exercise at 0.08 m s-1 (166% maximum aerobic speed) was alternated with 30 s of rest, distance capacity increased to 271 m, 4.5-fold greater than continuous locomotion at the same average speed (83% maximum aerobic speed). A 30-s pause following a 30-s exercise period was sufficient for maintaining low lactate concentrations in muscle and for partial resynthesis of arginine phosphate. A greater dependency on nonoxidative metabolism due to slowed oxygen uptake kinetics at low temperature resulted in a decreased duration of the critical exercise period, which increased performance relative to that measured at higher temperatures (30 s at 15°C vs. 120 s at 24°C). Despite the ghost crab's limited aerobic capacity at 15°C, distance capacity during intermittent locomotion at low temperature can be comparable to that of a crab moving continuously at a body temperature 10°C Warmer. While endurance capacity is generally correlated with maximum aerobic speed, we have demonstrated that both locomotor behavior and body temperature must be considered when characterizing performance limits.
• Weinstein, R., & Somero, G. (1998). Effects of temperature on mitochondrial function in the Antarctic fish Trematomus bernacchii. Journal of Comparative Physiology - B Biochemical, Systemic, and Environmental Physiology, 168(3). doi:10.1007/s003600050136
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  Effects of temperature on O2 consumption by mitochondria of the Antarctic fish Trematomus bernacchii were compared with effects obtained with mitochondria from tropical (Sarotheridon mossambica) and temperate zone fishes (Sebastes carnatus and Sebastes mystinus). Arrhenius plots of O2 consumption versus temperature exhibited slope discontinuities ('breaks') at temperatures (Arrhenius break temperatures: ABTs) reflective of the species' adaptation temperatures. The ABT for mitochondria of T. bernacchii is the lowest reported for any animal and is ~12 °C below the value predicted by a regression equation based on ABT data for several invertebrates and fishes. The temperature at which the acceptor control ratio (ACR), an index of efficiency of coupling of electron transport to synthesis of ATP, began to decrease with rising temperature also reflected adaptation temperature. The decrease in ACR with rising temperature began at ~18 °C for mitochondria of T. bernacchii, in contrast to ~35 °C for mitochondria of Sarotheridon mossambica. Maintaining T. bernacchii at 4 °C for 2 weeks led to no changes in ABT or in the response of ACR to temperature. The thermal sensitivities of mitochondria of T. bernacchii reflect the high level of cold adaptation and stenothermy that is characteristic of Antarctic Notothenioid fishes.
• Scholnick, D., Weinstein, R., & Gleeson, T. (1997). The influence of corticosterone and glucagon on metabolic recovery from exhaustive exercise in the desert iguana Dipsosaurus dorsalis. General and Comparative Endocrinology, 106(2). doi:10.1006/gcen.1996.6866
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  The skeletal muscles of ectothermic vertebrates possess an elevated glyconeogenic capacity that is responsible for a major portion of lactate removal and glycogen resynthesis following exercise. In lizards, changes in plasma hormone levels and the influence of differing hormone levels on muscle metabolism postexercise are poorly understood. We measured the effects of 5 min of exhaustive exercise on plasma levels of glucagon and corticosterone in the desert iguana Dipsosaurus dorsalis. We also determined the extent to which these hormones influence, or are influenced by, postexercise plasma lactate concentrations postexercise. Exercise resulted in the accumulation of 20 mM blood lactate, while plasma glucose levels remained stable throughout 90 min of recovery. Plasma glucagon was elevated sevenfold during 5 min of exercise and returned to resting levels within 45 min of recovery. Glucagon stimulated lactate incorporation into glycogen in isolated red muscle fiber bundles. Plasma corticosterone was also elevated to three times normal resting values, but only after 45 min of recovery. Blocking corticosterone elevation with metyrapone did not alter the kinetics of plasma lactate removal. In lizards, the dramatic rise in plasma glucagon occurs at the same time as previously reported elevated skeletal muscle glyconeogenesis and elevated glucagon stimulates lactate removal in vitro, strongly suggesting a role for glucagon in postexercise skeletal muscle metabolism.
• Weinstein, R., Slentz, M., Webster, K., Takeuchi, J., & Tischler, M. (1997). Lysosomal proteolysis in distally or proximally denervated rat soleus muscle. American Journal of Physiology - Regulatory Integrative and Comparative Physiology, 273(4). doi:10.1152/ajpregu.1997.273.4.r1562
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  We examined the mechanism of accelerated proteolysis in denervated rat soleus muscles. The soleus was denervated by severing either the tibial nerve (proximal, short stump) or sciatic nerve (distal, long stump) at 24, 48, 72, or 96 h before excision. Twenty-four hours after denervation, the extent of atrophy was similar for proximal and distal denervation, although lysosomal latency declined in both groups. After 48 and 72 h, denervation resulted in a decline in protein content, an increase in in vitro protein degradation, and a decline in lysosomal latency, all of which were greater in proximally denervated than in contralateral distally denervated muscles. These differences between acute responses of proximally and distally denervated muscles suggest the retention of some factor in the longer nerve stump that attenuates atrophy. After 96 h, total protein loss, protein degradation, and lysosomal latency were similar for proximal and distal denervation, suggesting the loss of axoplasmic flow from the long nerve stump.
• Weinstein, R. (1995). Locomotor behavior of nocturnal ghost crabs on the beach: Focal animal sampling and instantaneous velocity from three-dimensional motion analysis. Journal of Experimental Biology, 198(4).
• Autumn, K., Weinstein, R., & Full, R. (1994). Low cost of locomotion increases performance at low temperature in a nocturnal lizard. Physiological Zoology, 67(1). doi:10.1086/physzool.67.1.30163845
• Full, R., & Weinstein, R. (1992). Integrating the physiology, mechanics and behavior of rapid running ghost crabs: Slow and steady doesn't always win the race. Integrative and Comparative Biology, 32(3). doi:10.1093/icb/32.3.382
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  In 1979 Bliss predicted that, "land crabs are and will undoubtedly continue to be promising objects of scientific research." Studies of rapid running ghost crabs support her contention and have resulted in several general findings relating to locomotion and activity. 1) Energy exchange mechanisms during walking are general and not restricted to quadrupedal and bipedal morphologies. 2) "Equivalent gaits," such as trots and gallops, may exist in 4-, 6- and 8-legged animals that differ greatly in leg and skeletal (i.e., exo- vs. endoskeletal) design. These findings support the hypothesis that terrestrial locomotion in many species can modeled by an inverted pendulum or spring-mass system. 3) An open circulatory system and chitin-covered gills do not necessarily limit the rate at which oxygen consumption can be increased or the factorial increase oxygen consumption over resting rates. 4) Interspecific and intraspecific i.e., ontogenetic) scaling of sub-maximal oxygen consumption and maximal aerobic speed can differ significantly. 5) Locomotion at speeds above the maximal aerobic speed requiring non-aerobic contributions may be far more costly than can be predicted from aerobic costs alone. The cost transport may attain a minimum at less than maximum speed. 6) The speed which elicits maximal oxygen consumption during continuous exercise is attained at moderate walking speeds in crabs and probably other ectotherms. Speeds 15- to 20-fold faster are possible, but cannot be sustained. 7) The low endurance associated with the low maximal oxygen consumption and maximal aerobic speed of ectotherms moving continuously can be increased or decreased by altering locomotor behavior and moving intermittently. Ectotherms can locomote at high speeds and travel for considerable distances or remain active for long periods by including rest pauses. Alternatively, intense activity with extended exercise periods with short pause periods may actually reduce behavioral capacity or work accomplished relative to continuous activity during which the behavior is carried out at a lower intensity level without pauses. © 1992 by the American Society of Zoologists.
• Weinstein, R., & Full, R. (1992). Intermittent exercise alters endurance in an eight-legged ectotherm. American Journal of Physiology - Regulatory Integrative and Comparative Physiology, 262(5). doi:10.1152/ajpregu.1992.262.5.r852
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  Most animals move intermittently, yet many proposed performance limitations of terrestrial locomotion are based on steady-state measurements and assumptions. We examined the effect of work-rest transitions by exercising the ghost crab, Ocypode quadrata (28.1 ± 8.1 g), intermittently on a treadmill at 0.30 m/s, a supramaximal speed [i.e., greater than the speed that elicits the maximal rate of oxygen consumption (V̇O2)]. Duration of the exercise and pause periods, ratio of exercise to pause, and speed during the exercise period were varied to determine the effect on performance. Crabs fatigued after 7.5 min of continuous running, a distance capacity (i.e., total distance traveled before fatigue) of 135 m. When the task was done intermittently with 2-min exercise and 2-min pause periods, the crabs fatigued after 87 min (a total distance of 787 m), representing an 5.8- fold increase in distance capacity compared with continuous exercise at the same absolute speed (0.30 m/s) and a 2.2-fold increase in distance capacity compared with continuous exercise at the same average speed (0.15 m/s). Pause periods